Since 2005, we have prospectively identified 2 infants with [beta]-cystathionine synthase deficiency, 1 with MTHFR deficiency, 1 with Cbl G deficiency, 2 with methylmalonyl-CoA mutase deficiency, and 7 with Cbl C deficiency, as well as 8 mothers with vitamin [B.

Methylmalonic Acidemias [Adenosylcobalamin Synthesis Defects (CblA and CblB) and Methylmalonyl-CoA Mutase Deficiencies (mut- and mut+)]--An enzymatic defect in the oxidation of amino acids is the cause of these conditions, with an incidence of 1 in 50,000 to 1 in 100,000 live births.

Alternatively, female sex hormones may cause intracellular cobalamin redistribution favoring supply of cobalamin as a cofactor for methionine synthase at the expense of the methylmalonyl-CoA mutase reaction.

An example is increased propionylcarnitine (C3-acylcarnitine), a finding that requires differentiation of several disorders: propionyl-CoA carboxylase deficiency, methylmalonyl-CoA mutase deficiency, several cobalamin disorders, and even dietary deficiency of vitamin B1, This requires the expertise of clinical and biochemical geneticists and a variety of diagnostic tests.

It is possible that the two enzymes that require cobalamin, methionine synthase (which requires methyl-cobalamin) and methylmalonyl-CoA mutase (which requires adenosyl-cobalamin), behave differently in their response to the declining availability of cobalamin.

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